METHOD OF HYDROMETALLURGICAL PRODUCTION OF ZINC OXIDE Russian patent published in 1999 - IPC

FIELD: hydrometallurgy. SUBSTANCE: zinc is isolated from zinc-containing silicate material in three steps. First, starting material ground to fineness below 0.074 mm is subjected to autoclave leaching with sodium hydroxide solution and undissolved residue is separated. Residue is then mixed with calcium oxide observing ratio CaO/SiO₂ equal to (1-1.5):1 and free alkali content 5-10 wt %. Mixture is caked at 850-1000 C, crushed to fineness below 0.044 mm, and leached with return sodium hydroxide solution with concentration 270-350 g/l at solids-to-liquid ratio 1:(3-6). Precipitate is separated, washed, treated with sulfuric acid at pH 1-1.5, after which pH of solution is adjusted to 4.3-4.5. Acidic solution is filtered and combined with alkaline silicon-free solutions and wash waters maintaining concentration of sodium hydroxide in combined solution equal to 80-170 g/l to precipitate zinc oxide. The latter is filtered off, washed, dried, and calcined. Method enables more than 98.5% of zinc to be recovered from silicate-containing materials with more than 10 wt % zinc oxide and high portion of hard to uncover zinc compounds, recovered zinc purity being at least 98.5 wt %. EFFECT: increased zinc recovery and purity of product. 3 cl, 1 dwg, 1 tbl, 4 ex